Often not getting notifications for new posts on both forums I follow

It's happening again! After not changing any settings or setting any other email as spam, I will out of the blue just stop getting notified when there are new posts on either or both forums I follow, then it will resume after a period of time. This period of time can range anywhere from a few hours to several days. I always click the "view this thread" when I get a new notification. While writing this post, I just got a new notification on one of the forums, but there were 3 pages of new posts on the other forum for which I was not notified. They never go to the spam folder. I always keep the last post up so I can check on it when I don't have timely new posts, and routinely there will be new posts for which I was not notified. This is an on-going problem that has been happening for 2 years now. It would be a major disruption for me to have to change my email provider, and I don't have this problem with anyone else who emails to me.